ASoC: cs35l41: Change monitor widgets to siggens

Currently the internal monitor sources are input widgets, which means
if the card is set to fully routed these will not enable unless connected
to something in the machine driver. However, all these are internal
monitor signals so it makes no sense to connect them to something in the
machine driver. As such switch them to siggen widgets which will have
the same behaviour except not require external linkage on a fully routed
card.

Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: David Rhodes <drhodes@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20211029214028.401284-1-drhodes@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>